Beyond Spacetime — Part Two: What Would It Take for Quantum Physics to Explain Gravity?
From philosophical questions to physical principles
Introduction
In the first part of this investigation, we considered whether spacetime geometry might emerge from deeper quantum relationships rather than exist as an entirely fundamental feature of the universe.
The discussion began with questions about time, quantum fluctuations and the possibility that matter changes the physical properties of its surroundings.
Several preliminary mathematical approaches were investigated, but none established an independent explanation of gravity.
Some reproduced familiar gravitational relationships, although only after important assumptions had been introduced. Others produced results that did not agree with the behaviour required by observation.
These investigations raised an important question.
If gravity does emerge from quantum physics, what would a successful explanation have to demonstrate?
This paper examines that question without proposing another theory.
Its purpose is to distinguish established physical knowledge from philosophical possibilities and to identify the principles that any deeper explanation would need to satisfy.
1. What Would It Mean to Explain Gravity?
General relativity describes gravity through the geometry of spacetime.
Matter and energy influence that geometry, while the geometry determines the motion of freely falling objects and the propagation of light.
This description has been extraordinarily successful.
However, we can distinguish between describing gravitational behaviour and explaining whether spacetime geometry has a more fundamental origin.
Consider temperature.
Thermodynamics describes temperature and heat without requiring a detailed account of individual molecules.
Statistical mechanics provides a deeper explanation by relating those properties to microscopic behaviour.
Could spacetime geometry have a similar relationship with quantum physics?
Perhaps Einstein's equations describe the large-scale behaviour of something more fundamental.
This possibility does not imply that general relativity is incorrect.
Newton's equations remain useful even though Einstein subsequently provided a more general description of gravity.
A deeper understanding of spacetime might similarly preserve general relativity within its established domain.
But the analogy with thermodynamics is not itself evidence that spacetime is emergent.
That possibility must be established independently.
2. What Do We Know About the Quantum Vacuum?
Quantum field theory describes particles and their interactions through quantum fields.
Even when a field is in its lowest-energy state, its quantum properties can possess nonzero correlations.
The average value of a field may be zero while statistical relationships between measurements remain.
This is established quantum physics.
However, these fluctuations should not automatically be imagined as tiny classical objects continuously vibrating inside empty space.
Nor do quantum correlations necessarily imply a physical force connecting distant objects.
They describe relationships between quantum measurements.
Nevertheless, the quantum vacuum is more sophisticated than the classical picture of completely empty space.
This raises a question.
Could its correlations have something to do with the structure of spacetime?
There is an important difficulty.
In conventional quantum field theory, spacetime geometry is normally specified before the quantum correlations are calculated.
A theory of emergent spacetime would need to explain how geometrical relationships arise without simply assuming the geometry they are supposed to produce.
That is the central challenge.
3. Can Matter Change Quantum Correlations?
Matter interacts with quantum fields.
These interactions can change quantum states, fluctuations and correlations.
It is therefore reasonable to investigate whether matter changes certain quantum relationships in its surroundings.
But we must make an important distinction.
Changing a quantum correlation is not automatically equivalent to changing spacetime geometry.
Quantum states can change without producing a new gravitational field.
To explain gravity, we would need to identify a relationship through which quantum properties determine physical distances, clock intervals and the behaviour of freely falling objects.
This relationship would have to follow from independently justified principles.
We could not simply choose it to reproduce Einstein's equations.
Otherwise, we would have constructed another mathematical description of gravity rather than discovered its underlying mechanism.
4. The Special Problem of Time
Time is particularly difficult because we usually understand it through the physical processes used to measure it.
An atomic clock measures elapsed time through regular quantum behaviour.
Planck's relationship connects energy and frequency:
E = hf
This tells us something fundamental about quantum systems.
But it does not establish that time itself is generated by quantum oscillations.
Relativity provides another important fact.
Identical clocks following different paths through spacetime can accumulate different amounts of proper time.
Proper time is the elapsed time measured along a clock's own path.
It is not simply the frequency of a particular atomic transition.
Suppose a hypothetical quantum interaction changed the frequency of an atomic clock.
Would that demonstrate a change in proper time?
Not necessarily.
It might simply represent an additional physical interaction affecting that clock.
A genuine gravitational explanation must account for the consistent behaviour of different kinds of clocks, freely moving matter and light.
The challenge is therefore not merely to explain why atomic clocks change their relative rates.
It is to explain why measurements of space, time and motion fit together within one relativistic structure.
Could that structure emerge from deeper quantum relationships?
This remains an open question.
5. Why Space and Time Must Be Considered Together
Our earlier investigations encountered an important difficulty.
It was possible to construct mathematical models that reproduced gravitational time dilation.
But those models did not automatically explain the spatial geometry required by general relativity.
Light bending, planetary motion and other gravitational effects depend on the relationship between spatial and temporal geometry.
A model that changes clock rates without producing the correct spatial behaviour cannot explain gravity completely.
The reverse is also true.
This suggests that a deeper physical explanation must account for space and time together.
Most importantly, it must explain why their geometrical relationships have the particular form observed in nature.
Those relationships cannot simply be introduced as assumptions.
They must emerge from the proposed underlying physics.
6. Why Gravity's Universality Matters
One remarkable property of gravity is the universality of free fall.
Objects of different compositions fall with essentially the same acceleration when other forces can be neglected.
This behaviour has been tested with extraordinary precision.
The MICROSCOPE satellite experiment compared the free-fall behaviour of titanium and platinum test masses.
Its final results, published in 2022, found no violation of the weak equivalence principle at approximately the one-part-in-10^15 level.
Any proposed explanation of gravity must account for this universality.
That is particularly challenging for theories based on quantum interactions because different particles possess different properties.
Electrons, protons, neutrons and photons do not all participate in the same interactions in identical ways.
Yet gravity displays a remarkably universal character.
A successful underlying mechanism must explain why gravitational behaviour is largely independent of the detailed composition of matter.
It must also reproduce the observed behaviour of clocks and light.
Simply assigning different interactions to different particles and adjusting them to obtain the correct results would not provide a satisfactory fundamental explanation.
7. What Did Our Unsuccessful Models Teach Us?
Our earlier mathematical investigations produced several useful lessons.
The first concerned a hypothetical oscillating vacuum field.
We discovered that such a field could reproduce familiar gravitational relationships when suitable assumptions were introduced.
However, some of those assumptions effectively contained the geometrical relationships we were trying to explain.
Consequently, the model did not independently derive gravity.
A second approach involved quantum vacuum correlations.
In one simple calculation, a matter-induced change in the local field fluctuation decreased with the cube of the distance.
This did not provide the inverse-distance gravitational potential required by the proposed direct connection.
But the result concerned one particular interaction and one particular quantum quantity.
It did not prove that every possible correlation-based explanation of gravity must fail.
Other field mechanisms can produce long-range effects with different distance dependencies.
The lesson is that a proposed mechanism must naturally produce the correct gravitational behaviour without inserting it beforehand.
We also encountered questions concerning energy conservation and relativity.
A coherent oscillation extending throughout space could identify a preferred reference frame.
Although relativistic theories can contain oscillating fields, such a background is not automatically equivalent to the usual Lorentz-invariant quantum vacuum.
These difficulties exposed weaknesses in our assumptions.
They were not successful explanations of gravity, but they were useful investigations.
They helped distinguish mathematical agreement from physical explanation.
8. Conservation Laws and Relativity
Any deeper explanation of gravity must be compatible with established conservation principles.
Matter and fields may exchange energy and momentum.
However, the complete theory must consistently account for these exchanges.
In general relativity, local energy-momentum conservation is expressed through the geometry of spacetime.
Global energy conservation is more complicated in a general curved or expanding universe, where a universal conserved total energy need not be available.
A proposed quantum mechanism must respect these distinctions.
Relativity imposes equally important requirements.
We cannot introduce a universal physical clock or preferred frame without explaining how its effects remain consistent with experimental observations.
Quantum correlations provide a potentially useful starting point because they need not involve a coherent universal oscillation.
But correlations alone do not establish gravitational dynamics.
A successful theory would need to reproduce the causal structure of spacetime, the behaviour of moving observers and the known gravitational interaction of matter and light.
9. What Can Existing Research Teach Us?
Professional physicists have already investigated whether gravity might emerge from deeper physical principles.
In 1995, Ted Jacobson showed how Einstein's equations could be obtained from thermodynamic reasoning.
His argument assumed a relationship between horizon area and entropy, together with a thermodynamic relationship involving energy flow.
This suggested that gravitational equations might be understood as describing collective physical behaviour.
However, the argument relied on important assumptions involving spacetime geometry and horizon thermodynamics.
In 2010, Mark Van Raamsdonk investigated relationships between quantum entanglement and the connectivity of spacetime.
His work suggested that entanglement could play an important role in maintaining connected geometry within particular approaches to quantum gravity.
This was an important conceptual development, but it did not demonstrate that ordinary vacuum correlations independently generate the spacetime of our universe.
In 2016, Jacobson investigated a further relationship between vacuum entanglement and Einstein's equations.
His analysis used an equilibrium principle involving small spacetime regions and their entanglement entropy.
For certain quantum fields, this produced a particularly strong relationship between the equilibrium condition and the gravitational equations.
Again, important geometrical and physical assumptions remained.
These studies are encouraging, but their precise achievements matter.
They show that connections between quantum information, thermodynamics and gravitational geometry are mathematically meaningful.
They do not establish a complete microscopic mechanism explaining the origin of spacetime.
That distinction is essential.
10. What Does Emergent Spacetime Actually Mean?
The expression "emergent spacetime" can describe several different possibilities.
We might be attempting to explain physical distance.
We might instead be investigating the origin of clock intervals, the causal relationship between events, or the gravitational dynamics that connect matter with geometry.
These are related questions, but they are not identical.
A quantum model might produce a useful notion of distance without explaining gravitational acceleration.
Another might reproduce gravitational field equations while leaving the physical origin of proper time unresolved.
A complete theory would need to connect these properties consistently.
This distinction has also been emphasised in recent philosophical research.
In their 2026 paper, "The Many Problems of Spacetime Emergence in Quantum Gravity," Rasmus Jaksland and Kian Salimkhani argue that the general expression conceals several distinct questions.
Their analysis encourages researchers to specify exactly which aspect of spacetime they are attempting to explain.
This is a useful lesson for our investigation.
Instead of asking whether quantum physics can create spacetime in one enormous step, it may be more productive to investigate individual properties and determine how they are connected.
11. What Would Count as Genuine Progress?
A philosophical explanation can suggest possibilities.
A physical theory must eventually provide mathematical relationships that can be tested.
A successful proposal should explain known observations without introducing assumptions chosen merely to reproduce the expected answers.
Ideally, it should also produce a distinctive, testable prediction.
However, theoretical progress can also arise from deriving established physical relationships through independently justified principles.
The important word is independently.
A proposed theory should not assume the gravitational geometry that it claims to explain.
Nor should it introduce arbitrary constants simply to obtain the measured strength of gravity.
A meaningful explanation would identify the relevant physical structure, demonstrate its response to matter and show how geometrical behaviour follows.
It would need to explain gravity's universality, light propagation, clock behaviour and the conservation of energy and momentum.
These requirements provide a useful standard against which future proposals can be judged.
12. A More Productive Question
Our investigations suggest that a narrower question may be more useful than attempting another complete theory of gravity.
Can established quantum relationships independently determine any measurable aspect of spacetime geometry?
For example, could a quantum system provide a physical measure of distance or causal relationships without assuming that measure beforehand?
If so, could these relationships eventually be connected with gravitational dynamics?
We must be careful about what such a result would demonstrate.
Reconstructing geometry from quantum correlations calculated on an already assumed spacetime would not, by itself, prove that geometry is fundamentally emergent.
We would need to establish why the quantum relationships exist and how they determine the measurements of space and time.
This is a demanding objective.
But it offers a clearer research direction than introducing another hypothetical vacuum oscillation and attempting to make it reproduce Newton's equations.
If the quantum relationships cannot provide an independent explanation, we should recognise that limitation.
If they can, we would then have a foundation on which further physical questions could be investigated.
Conclusion
The possibility that spacetime geometry emerges from deeper quantum relationships is a serious philosophical and scientific question.
But imagining such a relationship is not the same as demonstrating it.
Our earlier mathematical investigations revealed how easily familiar gravitational equations can be reproduced once suitable assumptions are introduced.
They also demonstrated that apparently reasonable mechanisms can produce incorrect gravitational behaviour.
These difficulties are instructive.
They suggest that genuine progress depends on identifying independently justified physical principles rather than constructing equations to match known results.
Any successful explanation must account for gravity's universality, the relationship between spatial and temporal geometry, conservation laws and the observed behaviour of matter and light.
Research into thermodynamics, quantum entanglement and emergent spacetime provides useful starting points.
But a complete explanation remains unavailable.
Perhaps spacetime geometry is fundamental.
Perhaps it emerges from quantum relationships.
Perhaps the familiar distinction between matter and spacetime reflects a deeper physical structure that has not yet been discovered.
The purpose of this paper is not to decide between these possibilities without sufficient evidence.
It is to identify what would be required to investigate them scientifically.
The most important question may therefore be not simply whether quantum physics can reproduce Einstein's equations.
It may be whether quantum physics can explain why the universe possesses the particular geometry that those equations describe.
That is a question worth pursuing carefully, even if the eventual answer differs from our original expectations.
Selected References
Ted Jacobson (1995). "Thermodynamics of Spacetime: The Einstein Equation of State." Physical Review Letters.
https://doi.org/10.1103/PhysRevLett.75.1260Mark Van Raamsdonk (2010). "Building up spacetime with quantum entanglement." International Journal of Modern Physics D.
https://arxiv.org/abs/1005.3035Ted Jacobson (2016). "Entanglement Equilibrium and the Einstein Equation." Physical Review Letters.
https://doi.org/10.1103/PhysRevLett.116.201101Touboul and colleagues (2022). "MICROSCOPE Mission: Final Results of the Test of the Equivalence Principle." Physical Review Letters.
https://doi.org/10.1103/PhysRevLett.129.121102Bothwell and colleagues (2022). "Resolving the gravitational redshift across a millimetre-scale atomic sample." Nature.
https://doi.org/10.1038/s41586-021-04349-7Rasmus Jaksland and Kian Salimkhani (2026). "The Many Problems of Spacetime Emergence in Quantum Gravity." The British Journal for the Philosophy of Science.
https://doi.org/10.1086/727052
This paper is a philosophical investigation into the foundations of physics. It does not present a new experimentally verified theory of gravity.
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